Magnetic materials



Aug. 28, 1951 H, LEVERENZ ET AL 2,565,861

' MAGNETIC MATERIALS Filed Sept. 26, 1947 4 Sheets-Sheet s near/r5 PERMEABILITV Zhwcntor Humbaldi Wllevarenz fler-l l'harvey C(ttomeg g-' 28, 1951 H. w. LEVERENZ ET AL 2,565,861

MAGNETIC MATERIALS Filed Sept. 26, 1947 *4 Sheets-Sheet 4 Patented Aug. 28, 1951 MAGNETIC MATERIALS Humboldt W. Leverenz and Robert L. Harvey, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application September 26, 1947, Serial No. 776,292

This invention relates to improved materials having relatively high magnetic permeability and, at the same time, desirably low loss values (high Q factor) at radio frequencies and to improved articles made of these materials.

Whenever Q values are discussed or stated throughout this specification, there is meant a numerical value found by dividing the radio frequency reactance by the resistance of a circuit in which the materials of the present invention are introduced as induction coil core bodies.

The present invention is an improvement over our previous invention disclosed in application, Serial No. 719,594, filed December 31, 1946. In the said previous application, compositions comprising mainly F8203 and MgO were described. To these basic materials small amounts of other oxides, such as A1203, could be added.

It has now been found that the addition of zinc oxide to the previous reaction mixtures results in the formation of reaction products having still further improved properties as regards magnetic permeability and low loss factor. It has also been found that ZnO may be substituted for the MgO, wholly or partially, and that certain other oxides may be substituted in whole or in part for the ZnO and others for the MgO. As disclosed in our above mentioned earlier application, there may also be added small percentages of A1203, GazOa or GdzOa, or combinations of these.

One object of the present invention is to provide improved compositions having relatively high magnetic permeabilities with desirably high Q factor as well.

Another object is to'provide materials having exceptionally high degrees of magnetic permeability with good temperature stability.

Another object of the invention is to provide improved materials having relatively high degrees of magnetic permeability and which can be formulated such that this permeability may have either a constant, positive, or negative temperature coeflicient within the usable temperature range of the equipment. I

Another object of the invention is to provide improved materials having relatively high magnetic permeabilities and which may be given ositive, negative or constant coefiicients of magnetostriction by proper selection of composition and temperature of crystallization.

Another object is to provide a system composed of a novel form of crystalline 2 Claims. (Cl. 252-625) 2 from which may be chosen compositions having very high effective magnetic permeability, high Q factor at broadcast frequencies and excellent temperature stability.

Another object is to provide a novel class of compositions in the group known as ferrites,

which have improved properties of both magnetic permeability and high Q factor along with other desirable properties.

Another object is to provide materials as above described, which can be compressed into shaped bodies before heating, to form products having greatly improved properties of magnetic permeability and high Q values of radio frequencies.

Still another object is to provide novel methods of preparing improved materials having high magnetic permeability or high Q value or both.

These and other objects will be more readily apparent and the invention will be better understood with reference to the following specification, including the drawings of which:

Fig. l is a graphical illustration of one modification of a system of which the compositions useful in the present invention are a part, together with indicated optimum values of magnetic permeability, without regard to optimum Q value, for compressed bodies made up of various compositions within the system,

Fig. 2 is a graphical illustration of the same system shown in Fig. 1 with indicated optimum values of Q factor without regard to optimum magnetic permeability for compressed bodies made up of various compositions within the system,

Fig. 3 is a graphical representation of data obtained by measuring the relative magnetic permeability of compressed bodies of several different compositions, within the scope of the present invention, maintained at various temperatures,

Fig. 4 is graphical representation of data obtained by measuring the relative magnetic permeability at various ambient temperatures of several different compressed bodies, each formed at a different heatin temperature but all having positions within the scope of the present invention.

Although the compositions, which are a part of the present invention, are difl'erent from those described in our previously mentioned co-pending application, Serial No. 719,594, the general method of preparation is the same as illustrated therein. Briefly, this method includes the intimate mixing of MgO, F9203 and ZnO, each in a flne state of subdivision, heating, preferably, a compressed body made of these oxides within a range of temperatures of about 900 C. to 1500 C. for from minutes to 2 hours in an oxidizing atmosphere and then cooling. Optimum conditions of time I and temperature of heating will vary with each specific composition possible within the system of compositions which is a part of the present invention and with any one specific composition the optimum heating time decreases as the temperature of heating increases. In general, however,

some improvement in results is obtained by selecting widely varying times and temperatures within the range specified even though these improvements will not be the maximum obtainable when a more careful choice is made. Good results can be expected with almost any of the compositions, if a heating time of about 1 hour is used, and a heating temperature of the order of 1200? C. has proved satisfactory, if not always best, with all of the compositions. The reaction '30 product which is formed in all instances is a composite homogeneous crystalline body which does not have the same stoichiometric proportion of oxygen to metals as is present in the mixture before heating, but the exact proportions of the elements present in the products is not known and cannotbe easily determined. Although the products resemble previously known ferrites to some extent, they are apparently difierent in structure, both chemically and physically, since their. electrical properties are strikingly difierent. It is evident, for example, that the crystalline structure of these materials is novel and that the properties depend to some degree on the extent to which the crystalline structure is permitted to develop.

The oxidizing atmosphere in which the heating of the reaction mixture takes place may be supplied by passing a stream of oxygen through the reaction chamber. Less desirably, air may be used in place'of oxygen. It is also possible to phere .and as the hydroxide or carbonate, etc., if either an oxidizing or a neutral atmosphere is present. The other ingredients may also be present in forms such as hydroxides, acetates or carbonates which will revert to the desired oxide form when heated strongly in either an oxidizing or neutral atmosphere.

As previously stated, it is preferable, from a practical standpoint, to form compressed bodies of the reactants at pressures of say 20.000 p. s. i. and treat these bodies at elevated temperatures in order to impart the desired properties of increased permeability and low loss. The fact that shaped bodies of the compressed material can be;

lower permeability hitherto present in materials.

of this nature. When the material is made in the form of compressed bodies, the pressure of forming may vary widely. Pressures of 2,000 p. s. i. have been found to produce'the same improved results as those ten times as great. In general, it may be said that the pressure of forming should be sufllcient to form a closely coherent body.

After the heat treatment is accomplished as described, the reaction product is preferably, although not necessarily, cooled very rapidly, as by subjecting it to a blast of air or quenching in water. Rapid cooling generally increases the permeability and low loss qualities above those values obtained when slow cooling is used.

The reaction mixture may be compressed into any desired shape before heating takes place in the reaction chamber. Thus, the powder may be formed into bars having either rectangular or cylindrical cross section, into toroidal forms or into flat slabs, etc., as illustrated in Figs. 6, 6A, 6B, and 60. When some of the forms, such as flat slabs, are heated, at the elevated temperatures required, considerable warping may ordinarily occur. It has been found possible to provide techniques for the forming of these shaped bodies in which distortion is either largely or completely eliminated. One of these techniques includes the mixing of small percentages of a form products having improved magnetic permeability and low loss by heating the oxides in a neutral atmosphere, such as helium or nitrogen, but the improvement is not as great as when an oxidizing atmosphere is used. In contrast to the use of either an oxidizing or a neutral atmosphere, the presence of a reducing atmosphere, such as supplied by carbon monoxide or hydrogen, in the reaction chamber, is distinctly detrimental if materials having high permeability are desired. Therefore. it may be said that the heating should take place in a non-reducing atmosphere, preferably at atmospheric, or higher, pressures.

As pointed out in our previously mentioned c0- pending application, it is possible to start with a mixture of materials in other than the oxide form in which they are present in the reaction product providing these starting materials will be changed to the specified oxide upon heating to thetemperatures, times and atmospheric conditions stipulated. For example, instead of starting with a mixture containing F6203 the iron may be in the form of ferrous oxide, or magnetite, providing that heating takes place in an oxidizing atmoslubricant with the powdered oxides and then compressing them into desired shape. The shaped body is then heated as usual and the lubricant is completely burned ofl. Stearic acid in percentages of about 4 or 5 percent of the oxides present has been found suitable. The percentages are not very critical. Another lubricant found usable in about the same percentages is composed of one part trigamine stearate to 4 parts of a microcrystalline wax such as Carbowax. The lubricant apparently has the function of permitting more intimate packing of the powdered oxides so that heating takes place more evenly throughout the body. Since the lubricant must be of such a, nature that it is completely volatilized during the subsequent heating it does not appear in the final reaction product.

Another improvement 'in molding technique which was found to produce unexpectedly improved results is a feature of the present invention. The material is first placed in the mold and compressed at the usual high pressures. Then the pressure is released uniformly, as by hydraulic means, throughout the mold area.

aaeaeei 8 This has been found togreatly reduce ,warpins tendencies when the material is later heated at high temperatures and then cooled.

The manner in which the optimum magnetic permeability lb of the compositions, made according to the present invention, varies with the pro-- portions of the three main ingredients present in the reaction mixture is illustrated in Fig. 1. This figure, first of all, represents all possible combinations within the ternary system F8203 :MgO ZnO Upon this system representation have been superimposed curves, each of which shows all compositions found to have a particular value of relative permeability, which value is the number given to the curve. For example, the curve designated (2) has been drawn through all points representing all compositions of the reaction mixture having a relative permeability equal to 2 when the mixture is compressed and crystallized as described. Absolute permeability values p. are considerably in excess of those shown on the curves. All compositions tested were formed by mixing the oxides as previously described, forming each sample into a short bar 1% inches long, having a cross section 0.1 inch square, by molding at 20,000 p. s. 1. pressure and heating at temperatures ranging from 1100 to 1400 C. All measurements were made at room temperature of about 25 C. by inserting the bar within a uniformly wound coil slightly larger in diameter than the thickness of the bar and using a fre-' quency of about 600 kilocycles. A powdered iron core of similar dimensions was used as a reference standard. The reference core exhibited a relative permeability a under similar conditions of about 5.7. The test coil, alone, which was constructed of 186 turns of'No. 005 copper wire, in-

side diameter 341", and had a Q value of 60 and the resonanttesting circuit was tuned by a shunt capacitance of 100 f. Samples were tested of each composition which had been fired at various temperatures within the range specified and those having the highest values of a for each composition were selected for purposes of illustration without regard to their Q values when tested in a resonant circuit.

It can readily be seen from the figure that those reaction mixtures having appreciable percentages of all three of the oxides produced reaction products having the highest. permeability values. However, the optimum amount of ZnO to be added to the FeaOa-MgO reaction mixture depends upon the relative proportions of the latter two ingredients present. Referring to curve (I3) of Fig. 1, for example, it can be seen that a compressed body having a relative permeability of 13 may be constituted by the reaction product produced by treating a mixture containing the relative proportions of 05 mole part Fezos, 0.34 mole part MgO and 0.16 mole part ZnO. Referring to the same curve (l3)"it can.

also be seen that a product having the same relative permeability may be made from a reaction mixture made up of the relative proportions of 0.46 mole part F6203, 0.25 mole part MgO and 0.29 mole partZnO.

The closeness with which curves (8), (9) and (I0) approach the MgO-FezO: axis brings out the fact that the addition of very small mole proportions of ZnO to the MgO-FezOa mixture produces significant increases in the permeability of the product, the lower limits of significance appearing to be about one mole per cent.

The data illustrated on Fig. 1 also show that additions of ZnO, in amounts of more than about 0.45 mole part on a basis of 0.55 mole part for the sum of the other two oxides, produces no improved results in products operated at room tem perature. Stated in other terms, the upper limit of ZnO should be about 45 mole per cent of the whole composition for room-temperature (or higher) operation.

Fig. 1 also illustrates that the compositions of the present invention should contain from about 30 to about mole per cent F8203, if superior permeability is desired, although curve (6) includes compositions having slightly less than 30 mole per cent FezOa.

Compositions according to the present invention may comprise FezOs and ZnO with no MgO present. As indicated in Fig. 1, certain compositions falling on the FezOs-ZnO axis have usefully high permeabilities and some of these have desirably high Q values as well. The figure indicates that the preferred compositions in the binary system are from 0.8FezOa-0.2Zn0 to about 0.6FezO:-0.4Zn0, or inother words, the reaction mixture should contain from 0.6-0.8 mole part FezOa and 0.4-0.2 mole part ZnO.

In those compositions having all three ingredients present, the amount of MgO may vary considerably, again depending upon the relative proportions of the F6203 and ZnO present. The smallest amounts of MgO which may be regarded as significant in replacing some of the ZnO is about 1 mole per cent while the highest amount of MgO found to be operative in the production of materials having high permeability is about 69 mole per cent in the ternary system. It is also apparent that MgO must be present in these compositions, providing no other oxides are considered except F6203 and 2110, if materials havin effective permeabilities of 11 or more are to be obtained.

As previously noted, the curves plotted in Fig. 1 have been drawn by selecting materials, heated within the range of 1100-1400 C., which exhibited the highest permeability values found for each tested composition within this heating range whether a correspondingly high Q value was found or not. However, for purposes of comparison the Q values of some of the compositions have been spotted throughout the figure. These values have been indicated thus; 100, with their numerical values underlined. These values were measured as later described in connection with Fig. 2.

One general aspect of the present invention, then, is the discovery that when intimate mixtures of either Fezoszzno or mixtures of F62O3ZZI1OIMgO are heated in a non-reducing atmosphere at from 900-1500 0., there are formed novel crystalline products which have novel properties not found when 'm'xtures of these oxides are heated under other conditions.

A specific aspect of the invention is the discovery that certain proportions of these oxides should be used within the ranges indicated in order to obtain products havin a higher magnetic permeability than materials heretofore commonly known and used.

Within the range of compositions previously delineated as having usefully high permeabilities. there may also be selected a preferred range of compositions having unusually high permeability values which adapt these materials to uses not meable materials heretofore in use. These comaccuser positions are reaction products selected from Fig. 1 and are encompassed within the polygons A and B. Those within the polygon A comprise 0.45-0.55 mole part Fesoi to 0.05-0.35 molepart ZnO and 0.1-0.50 mole part MgO. Those within the polygon B comprise 0.55-0.70 mole part P820: to 0.25-0.35 mole part ZnO and -0.2 mole part MgO.

For many practical uses within the field of radio or, more generally, electricity, including electronics, it is highly desirable that the products should have not only high magnetic per- A meability but a high Q factor at radio frequencies which may range from audio frequencies to about megacycles.

Fig. 2 is a plot based on the same general systemv of compositions illustrated in Fig. 1, with superimposed curves. each of which is drawn through all points exhibiting the same Q value. Again, the reaction products were prepared by heating the reaction mixtures at from 1100- 1400" C. and the ones exhibiting optimum results within this range selected without regard to their permeability values. Each curve is numbered with the corresponding Q value which it represents and it is readily apparent that the curves may not be continuous. Series of compositions isolated from each other may exhibit similar Q values. In general, it has been found, as illustrated in the figure, that the same general range of compositions which have been selected as having usefully high permeabilities also exhibit usefully high Q values.

Within the broader range of compositions having usefully high Q values, there maybe chosen a narrower preferred range of compositions having unusually high Q values which fit them for special applications in the electronics field. These compositions comprise 0.55-0.75 mole part FeaOa to 0.01-0.40 mole part ZnO and 0.05-0.44 mole part MgO. The area representing these preferred compositions is shown by the quadrilateral A within the system diagram of Fig. 2. For pur-" poses of illustration and for indicating the area of optimum ,uxQ several values of permeability indicated by underlined numbers have been spotted throughout the figure. I

All values shown in Fig. 2 were measured at about 600 km, the Q value of the measuring coil alone being 62 at 2.2 megacycles and the resonant testing circuit was tuned by a shunt capacitance of 100 m. All data were also takenat room temperature of about 25 C. and the dimensions of the cores and testing coil were the same as specified in connection 'with'the explanation of Fig. 15 t 'A study of Figs. 1 and 2 will show that the reaction products having the highest values of magnetic permeability do not usually have also optimum Q values. Therefore, it is not possible to pick out those compositions having the highes't effective permeability, say 15, and assume that they are the optimum for given application. But since many compositions having a permeability not far below the optimum found in the system also have a reasonably high Q value, it will usually be possible to compromise on products which do havedesirably high values in both respects. For example, a composition representing the reaction product of about 0.6 mole part FezQs, 0.2 mole part MgO and 0.2 mole part ZnO exhibits an eflective magnetic permeability of 10 and a Q value of 118. Other compositions may be selected having still higher permeabilities and only slightly Q values.

A range of preferred compositions having an unusually high product of nXQ is found within the larger system of compositions forming the basis of the presentinvention. These composimole part MgO with all proportions being un-' derstood to be approximate since no sharp line of demarcation has been found. These compositions are designated in Fig. 1 by the quadrilateral C.

Another importantfactor to be considered in selecting materials of this nature for practical.

applications within the electrical field isthelr stability within the expected range of operating temperatures. Fig. 3 is a graph of the variation of effective permeabilities of six different compositions within certain ranges of temperature. All of the compositions selected show sharp drops in permeability value within certain narrow temperture ranges. The temperature at which this sharp drop occurs for any particular composition is known as its Curie point. The Curie point is diflferent for each composition. It is the temperature above which thermal agitation interferes with the electron-spin orientations required for magnetism. As related to Figs. 1 and 2, all of the compositions plotted in Fig. 3 lie along the horizontal line 4.5-4.5 but the heating temperture in all cases was 1100 C. The relative proportions of each composition are expressed in mole parts.

Table of compositions plotted in Fig. 3

curve FezO; Mgo ZnO It is apparent that a given material should be used at temperatures below its Curie point if temperature stability is to be expected.

Another aspect of the invention is the discovery that the temperature of crystallizing the reaction product greatly influences the later performance of the material when it is subjected to changes in the ambient temperature. With any particular composition, it is possible to find, by'

experimenting with different temperatures of heating within the range previouslyspecified, a preferred heating temperature which will produce a product that will have a substantially constant permeability as a function of the ambient operating temperature from 20-80 C. It

has also been found possible with -a particular composition to find temperatures of heating which will produce reaction products having either positive or negative temperature coefficients of permeability. This is illustrated in Fig. 4. In this figure, all curves show eilective permeability plotted against change-in ambient temperature for a reaction product made by mix-' ing ferric, magnesium and zinc oxides in the proportion FezC .;:0.5Mg0:0.5Zn0 and crystallizing in an oxidizing atmosphere at three different temperatures. Curve (A) is a record of the variation in magnetic permeability of a core of the compressed reaction product, made up and tested as previouslly described, when the crystallizing temperature was 1100 C.- Curves (B) and (C) are similar curves plotted from cores heated at 1200 C. and 1300 C., respectively. The data shown in the figure illustrate the fact that a core of this particular composition prepared at a heating temperature of 1200 C. shows a substantially zero temperature coeflicient of permeability between 20 and 80 C. and that, therefore, this crystallizing temperature should be approximately adhered to, if good temperature stability is desired in the reaction product prepared from this particular composition. The figure also shows that cores of the same composition crystallized at 1100 C. exhibit negative temperature coeflicients of permeability and those crystallized at 1300 C. exhibit positive coefficients. It should be understood, however, that these temperatures are approximate, only, and that differences of a few degrees, either way, in the heating temperature will produce no significant changes in results. It should also be understood that the critical values will be different for different compositions and that the preferred values for any one composition can only be determined by experiment. In the examples illustrated, the time of heating was selected to produce materials having optimum permeability but other heating temperatures within the mevdian range give approximately the same results in this respect.

Figure is a plot of the relative Q values for the same cores, testing data for which are shown in Fig. 4, curve (D) being a plot of relative Q value as a function of ambient operating temperatures from 20-80 C. for the core crystallized at 1100 C. and curves (E). and (F) being test data obtained by measuring cores of the same initial composition heated at 1200 C. and 1300 C., respectively. It is noted that all cores having this composition exhibit negative temperature coefiicients with respect to their Q values within the operating temperature range specified, although the coefficients differ one from another. It has been found, additionally, that all cores do not exhibit negative coefficients when those of different compositions are tested. For example, a core made up of a starting mixture of Fez03:1.2MgO showed all positive coefiicients with regard to the Q value.

In addition to the control of the temperature coeflicients of permeability and Q values described above, it has also been found possible to provide materials having either positive, negative or constant coeflicients of magnetostriction by proper choice of composition and crystallization temperature in the FezOazMgOzZnO system. As an example, in the system FEzOaIMgO I ZnO those compositions containing about 0.5-0.75 mole part FezOa to 0.5-0.25 mole part of the sum of the other two oxides have been observed to have positive values of magnetostriction while those compositions having less than 50 mole per cent Fezoatend to have negative values of magnetostriction. For most practical applications, therefore, it is desirable to choose compositions within the former range when magnetostrictive properties are important.

Although, in the present invention, it is preferred to use compositions containing the 3 oxides MgO, ZnO and F8203, it has been found possible to substitute CdO for some or all of the ZnO in this system. The preparation of the materials is carried out in exactly the same manner as when ZnO is used and the preferred proportions of CdO fall within approximately the same limits as found for ZnO. The permeability values and Q values may be described as comparable although somewhat inferior to those found for compositions in which no CdO is used.

Another substitution which may be made within the scope of the present invention is the substitution of NiO in whole or in part for MgO. In a binary system containing only F6203 and N10, the preferred proportions of the ingredients are 0.4-0.53 mole part FezOa to 0.6-0.4? mole part NiO. This range is found by inspection of the MgO-FezOa axis of Fig. 1 since the NiO may be substituted for the MgQ without appreciable change in proportions. Although the usual chemical properties of magnesium and nickel differ widely, their ionic radii are about the same. Hence, in a crystalline network, nickelous ions would occupy about the same space dimensions as magnesium ions and this appears to account for the similarity of their electrical properties in the compositions of the present invention. As described in the previously mentioned co-pending application, Serial No. 719,594, there may be added small percentages of trivalent oxides from the class consisting of A1203, GaaOs and GdzOs to provide additional small improvements in permeability values and in other operating characteristics. The preferred range of amounts of the addition agents used is 0.01 to 0.10 mole, expressed as oxide, per mole F8203 present. A referred composition was made up by mixing 1 mole part F8203, 0.5 mole part MgO, 0.5 mole part ZnO and .015 mole part A1(OH)3, heating at 1100 C. for. 1 hour in compressed core form and cooling. The core had a relative permeability of 16 and a Q value of 35. I

There has thus been described a series of novel crystalline materials having strikingly improved properties with respect to magnetic permeability, Q value, and magnetostriction, which properties greatly enhance their value and broaden the scope of use of this class of material in the electronics field. Although several embodiments of our invention have been described, it will undoubtedly be apparent to those skilled in the art that equivalent forms are possible.

We claim as our invention:

1. An article of manufacture characterized by having a high effective magnetic permeability comprising a compressed body made up of a reaction product produced by heating an intimate mixture of 1 mole part F6203, 0.5 mole part MgO, 0.5 mole part ZnO and 0.015 mole part A1(OH)3 at about 1400 C. for about 1 hour in an oxidizing atmosphere.

2. A composition of matter consisting essentially of the reaction product produced by heating together in a non-reducing atmosphere at temperatures of from 900-1500 C. for from 10 minutes to 2 hours, an intimate mixture of 0.3-0.75 mole part FezOa, 0.01-0.69 mole part of a second ingredient which is at least one of a class consisting of magnesium and nickel oxides and 0.01-0.45 mole part of a third ingredient which is a mixture of zinc and cadmium oxides.

3. A composition according to claim 2 in which the proportions of the oxides in the reaction mixture comprise 0.45-0.55 mole part F8203 to 0.10-0.5 mole part of said second ingredient and 0.05-0.35 mole part of said third ingredient.

the proportions of the oxides of the reaction mixture compris 0.55-0.75 mole part F8203 to 0.05-0.44 mole part 'of said second ingredient and 0.01-0.4 mole part of said third ingredient.

5. A composition according to claim 2 in which the proportions oi the oxides of the reaction mixture comprise 0.47-0.63 mole part F6204 to 0.12-0.30 moi part of said second ingredient and 0.12-0.3 mole part of said third ingredient.

6. A composition of matter consisting essentially of the reaction product produced by heating together in a non-reducing atmosphere at a temperature of from 900 C. to 1500 C. for from ten minutes to two hours, an intimate mixture oi 0.3-0.75 mole part ferric oxide, 0.01-0.69.

mole part 01' a second ingredient which is at least one 01 a class consisting of magnesium and nickel oxides, 0.01-0.45 mole part of a third ingredient which is at least one of a class consisting 01' zinc and cadmium oxides and 0.01-0.10 mole part of a fourth ingredient which is at least one of a class consisting of aluminum, gallium and gadolinium oxides.

'l. A molded body 01 predetermined shape consisting essentially of a reaction product produced by 'heating together in a non-reducing atmosphere at a temperature between 900 and 1500 C. for from 10 minutes to 2 hours, an intimate mixture of 0.33-0.75 mole part Feaoa, 0.01-0.69-.

mole part of a second ingredient which is at least one of a class consisting of magnesium and nickel oxides and 0.01-0.45'mole part of a third ingredient which is a mixture of zinc and cadmium oxides.

8. A molded body according to claim 7 in which said second ingredient is magnesium oxide.

9. A molded body according to claim 7 in which.

said second ingredient is nickel oxide.

10. A molded body according to claim 7 in A .11. A molded body of predetermined shape consisting essentially of a reaction product produced by heating together in a non-reducing atmosphere at a temperature between 900 and 1500* C. i'or from 10 minutes to 2 hours, an intimate mixture of 0.3-0.75 mole part F6203, 0.01-0.69 mole part 01' a mixture of magnesium s21?! nickel oxides, and 001-045 mole part zinc o e.

12. A molded body of predetermined shape consisting essentially of a reaction product produced by heating together in a non-reducing atmosphere at a temperature between 900 and 1500 C. for from 10 minutes to 2 hours; an intimate mixture of 0.3-0.75 mole part Feaoa,

0.01-059 mole part of a.mixture of magnesium and nickel oxides. and 0.01-0.45 mole part cadmium oxide.

- HUMBOLDT w. LEVERENZ.

ROBERT L. HARVEY.

REFERENCES CITED The following references are of record in the file o! this patent:

UNITED STATES PATENTS OTHER REFERENCES Magnetic and Electrical Properties of the .Binary Systems IMO-F6203 by J. L. Snoek published in Physics. III, No. 6, June 1936, pages 481 and 482. r 

1. AN ARTICLE OF MANUFACTURE CHARACTERIZED BY HAVING A HIGH EFFECTIVE MAGNETIC PERMEABILITY COMPRISING A COMPRESSED BODY MADE UP OF A REACTION PRODUCT PRODUCED BY HEATING AN INTIMATE MIXTURE OF 1 MOLE PART FE2O3, 0.5 MOLE PART MGO, 0.5 MOLE PART ZNO AND 0.015 MOLE PART AL(OH)3 AT ABOUT 1400* C. FOR ABOUT 1 HOUR IN AN OXIDIZING ATMOSPHERE. 